In a bearing arrangement of the pre-cited type known from EP-A-0 249 674, the inner ring and the threaded spindle can rotate in a stationary housing. A rotary drive independent from the rolling elements is not provided for the inner ring and neither can it be accommodated because the spaces of the housing adjacent to the inner ring are occupied by roller carrier rings and are closed.
A bearing arrangement disclosed in EP-OS-0 743 470 uses a planetary transmission for converting the rotary motion of a rotor of a motor into a sliding motion of a spindle that actuates a brake. This planetary transmission permits the transmission of a large force to the brake disc by a small forward movement of the spindle due to the fact that the spindle has a fine thread with a very small thread pitch while the inner ring, which is configured as a spindle nut, has a coarse thread. The rolling elements are configured as roller bodies and are situated in the annular space between the spindle and the spindle nut. They circle round the spindle as planets during the rotation of the spindle nut and mesh with the threads of the spindle and the spindle nut and therefore require two different threads, a fine thread for meshing with the spindle and a coarse thread for meshing with the spindle nut. This arrangement therefore has the drawback of being very complicated and expensive.
The prior art inner ring configured as a spindle nut is surrounded by a pot-shaped brake piston attached to the threaded spindle. During the axial motion of the threaded spindle, the cylindrical wall of the brake piston slides with its inner surface along the inner ring and with its outer surface along the inner wall of the bore of the stationary housing in which these components are arranged. This results in a considerable loss of energy due to friction.
The mounting of the inner ring in the housing is effected with the help of the coupled rotor of the electromotor, said rotor comprising two ball bearings configured as radial bearings and one roller bearing configured as a thrust bearing.